linux-kernel - [RFC PATCH 0/3] block: Make old dio use iov_iter_extract

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Date:   Thu, 25 May 2023 16:50:59 +0100
From:   David Howells <dhowells@...hat.com>
To:     Christoph Hellwig <hch@...radead.org>,
        David Hildenbrand <david@...hat.com>
Cc:     David Howells <dhowells@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Hillf Danton <hdanton@...a.com>,
        Christian Brauner <brauner@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [RFC PATCH 0/3] block: Make old dio use iov_iter_extract_pages() and page pinning

Hi Christoph, David,

Since Christoph asked nicely[1] ;-), here are three patches that go on top
of the similar patches for bio structs now in the block tree that make the
old block direct-IO code use iov_iter_extract_pages() and page pinning.

There are three patches:

 (1) Make page pinning not add or remove a pin to/from the ZERO_PAGE,
     thereby allowing the dio code to insert zero pages in the middle of
     dealing with pinned pages.

 (2) Provide a function to allow an additional pin to be taken on a page we
     already have pinned (and do nothing for the zero page).

 (3) Switch direct-io.c over to using page pinning and to use
     iov_iter_extract_pages() so that pages from non-user-backed iterators
     aren't pinned.

Note that I haven't managed to test this yet as SELinux is refusing to let
me mount things like ext2 filesystems on account of it not having xattrs:-/

I've pushed the patches here also:

	https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=iov-old-dio

David

Link: https://lore.kernel.org/r/ZGxfrOLZ4aN9/MvE@infradead.org/ [1]

David Howells (3):
  mm: Don't pin ZERO_PAGE in pin_user_pages()
  mm: Provide a function to get an additional pin on a page
  block: Use iov_iter_extract_pages() and page pinning in direct-io.c

 fs/direct-io.c     | 68 ++++++++++++++++++++++++++++------------------
 include/linux/mm.h |  1 +
 mm/gup.c           | 54 +++++++++++++++++++++++++++++++++++-
 3 files changed, 95 insertions(+), 28 deletions(-)